Sediment, Stormwater, and Dam Safety Program Policy Memorandum #2 - Roadway/Railroad Embankments with Culvert Crossings (not “MDE Dam Embankment Guidance - Tech Memo # 2”) February 18, 2020
Presentation Outline I. MDE II. The ubiquitous CULVERT III. The PROBLEM that lead to Policy Memo #2 IV. The SOLUTION V. The PROCESS for evaluating a culvert crossing VI. Our OBJECTIVE and what YOU as a designer or reviewer can do to help
Changing of the Guard Boomers retire and millennials move in. Gen-xers bridge the transition.
Water and Science Administration Sediment, Stormwater, and Dam Safety Program Program Manager Jennifer Smith Administrative Specialist Michele Miles Deputy Program Manager Ray Bahr Dam Safety Dam Safety Inspections and Plan Review Division Program Review Division Permits Division Compliance Division Amanda Malcolm, Chief Stew Comstock, Chief John Roche, Chief Hal Van Aller, Chief Shanae Pettaway Kristen Jones Office Secretary Administrative Specialist Charlie Wallis Visty Dalal Vimal Amin Scott Bass Ethan Bright Deborah Cappuccitti RCE Senior - Vacant Anna Sobilo-Ryzner John Sodimu Dela Dewa RCE Senior - Vacant Kelly Flint Dan Laird Andrew Tagoe Hira Shrestha Collin Hiltner Brian Cooper Chimere Eaton Christina Lyerly Leah Wenck Michelle Crawford RCE I - Vacant Pat Depkin Nora Howard
Collaborative Efforts between Dam Safety Permits and Plan Review Division • Guidance on dam breach analysis (draft posted) • Policy/technical memos (some posted; more coming) • Small pond guidance (in progress) • SHA small pond delegation (in progress) • CMAC guidance (general guidance forthcoming) • Electronic approvals (in progress)
Technical Memoranda from the Plan Review Division
Policy Memoranda from MDE Dam Safety
Twin Box Culverts
Little Culvert
Historic Stone Culverts under Railroads
Video of Culvert Failure
“In Climate Change Preparation, the Humble Culvert is Key” Susan Sharon, Maine Public Radio Culverts must be adequately sized!
The PROBLEM Roadway/railroad embankments sometimes function as dams, intentionally or unintentionally, and they are not constructed to impound water. Culverts fail and dams fail, but the more water impounded behind the roadway/railroad embankment, the greater the hazard and the greater the likelihood of failure.
History – 1981 Drainage Manual
History
History
Federal Guidance – Highways as Dams https://www.fhwa.dot.gov/engineering/hydraulics/policymemo/20080910.cfm Highway Embankments versus Levees and other Flood Control Structures – September 10, 2008 Embankments and Permanent Dams The FHWA floodplain regulations do recognize that there are times when embankments may interact with or function as permanent dams. In these cases, the FHWA has no design standards. Instead the FHWA regulations require the design have the approval of the State or Federal Agency responsible for the safety of dams or like structures within the State. Even in this case, the FHWA floodplain regulations distinguish between permanent structures and those affected during floods.
The Problems with Culvert Crossings Functioning as Dams Pipe Embankment Hydraulic Capacity
The Conduit - Dam Spillway Pipe vs. Road Culvert Dam Spillway Pipe – Concrete cradle – ASTM C-361 concrete pipe – Watertight joints – Construction methods • Pipe laid prior/during embankment construction Roadway Culvert – No concrete cradle – Gravel bedding – Pipe material – Joints probably not watertight – Construction methods • Trench • Jack and bore
Dam Embankment – Materials – Construction – Foundation – Cutoff trench – Impervious core – Seepage Control – Freeboard Source: Paul Schweiger , Gannett Fleming, ASDSO, “Dam Failures and Lessons Learned”
Roadway Embankment ?
The Drivers • Poor submittals. • Debates over what Code 378 says. • MS4 restoration projects. • P3 push. The Purple Line. Desire to designate SHA as small pond approval authority. The need for clear and improved guidance. • Climate change, micro-bursts, more frequent and more severe flooding (like Ellicott City and SC).
Flood Damage from Crazy Weather
The SOLUTION Policy Memorandum #2! Basis of policy memo comes from COMAR, State law, Maryland Pond Code 378, Federal Highway Administration, ASDSO survey, Bureau of Reclamation, and policies in other states.
Culvert vs. Spillway? Roadway Embankment vs. Dam? Illinois: Intent, 1 foot of headwater Minnesota: Intent New Jersey: Hw – Tw < 5 feet Maryland: Intent, Hw-Tw < 10 ft, Hw/D < 2
Maryland Dam Safety Regulations Title 26 DEPARTMENT OF THE ENVIRONMENT Subtitle 17 WATER MANAGEMENT ADMINISTRATION Chapter 04 Construction on Nontidal Waters and Floodplains .02 Definitions. (4) "Dam" means any obstruction, wall, or embankment, together with its abutments and appurtenant works, if any, in, along, or across any stream, heretofore or hereafter constructed for the purpose of storing or diverting water or for creating a pool upstream of the dam, as determined by the Administration.
Policy Memo #2 - Roadway/Railroad Embankments with Culvert Crossings
Policy Memo #2 - Roadway/Railroad Embankments with Culvert Crossings
Dam Safety Permit A Dam Safety Permit is required for a dam higher than 20 feet. An application for a Dam Safety Permit is required for a conduit penetrating a roadway or railroad embankment higher than 35 feet.
20’x32' arch pipe with > 5000 ac -feet of storage at brim full embankment height = approximately 90 feet
Embankment Height = #$%^? For roadways: For railroads: H H The embankment height is measured The embankment height is measured from the lowest point of excavation or fill from the lowest point of excavation or fill on the upstream slope of the embankment on the upstream slope of the to the incipient point of overtopping. embankment to the subballast at the incipient point of overtopping. Referred to as the “REGULATORY HEIGHT”
Upper Limit The incipient point of overtopping may not occur on the same section as the culvert. Consider the profile of the roadway, not just the profile of the pipe. point of overflow lowest point of excavation
The engineer's wife A wife asks her husband, an engineer, "Darling, can you please go to the shop, buy one pint of milk, and if they have eggs, get a dozen!" Off he goes. Half an hour later the husband returns with 12 pints of milk. His wife stares at him and asks, "Why on earth did you get 12 pints of milk?" "Well… they had eggs" he replied. https://newengineer.com/insight/10-jokes-only-engineers-will-find-funny-1111728
Meaning of “or” and/or “and”???? A conduit penetrating a roadway or railroad embankment is considered a dam when any one of these three conditions exists: a. HW-TW >10 feet and HW depth /D > 2; or b. Permanent pool > 3 feet; or c. The culvert includes a structure to control water surface elevations. Conversely, a conduit penetrating a roadway or railroad embankment is considered a culvert when all four of these conditions are met: a. HW- TW ≤ 10 feet or HW depth /D ≤ 2; b. Permanent pool ≤ 3 feet; c. There is no structure to control water surface elevations; and d. The embankment height is ≤ 35 feet
Culvert Criteria A conduit penetrating a roadway or railroad embankment is considered a culvert when all four of these conditions are met: a. HW- TW ≤ 10 feet or HW depth /D ≤ 2; b. Permanent pool ≤ 3 feet; c. There is no structure to control water surface elevations; and d. The embankment height is ≤ 35 feet
Headwater (HW) and Tailwater (TW) TW elevation is lower than The head on the upstream invert embankment is elevation. HW depth. HW-TW = HW depth TW elevation is higher than The TW reduces the upstream invert head differential on elevation. the embankment. HW-TW = HW elev – TW elev
Design Capacity vs. Criteria for Evaluation MDE is not saying that culverts must be designed to convey 100- year storm. Design capacity is dependent on criteria for the class of road. From a dam safety perspective, the concern is not whether a road overtops for 100-year storm or even the 10-year storm. The concern is how much water is impounded behind the roadway or railroad.
Culvert locations that can be eliminated as dams based on geometry Assuming there is no control structure or no permanent pool deeper than 3 feet, then a crossing will not be considered a dam: if the distance from the upstream toe to if the crest of roadway/railroad the crest of the roadway/railroad is less embankment is ≤ 10 feet above the than twice the diameter of the pipe downstream toe < 10 ft < 2D Note that D = diameter of single pipe, not the effective diameter of three pipes.
A TRAIN IS COMING!!
Acceptable Hydrologic Modeling NRCS methodology (TR-55 and TR-20) - yes ✔ Routing that includes storage behind culvert - yes ✔ Rational Method - no ✖ PM #2 currently states that the Rational Method is acceptable for embankments under 35 feet, but that is going to be revised.
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